1. Field of the Invention
The present invention relates to a gloss-providing sheet for providing high gloss to a toner image on a recording material in which the gloss-providing sheet is placed on a toner image surface of the recording material such as paper and is heated so as to fuse toner, and then the gloss-providing sheet is separated from the recording material after the toner is cooled and solidified. Further, the present invention relates an image formation apparatus such as a copying machine, printer, facsimile machine, multi-function device thereof, and the like using such a gloss-providing sheet and more particularly to an image formation apparatus employing electrophotography.
2. Description of the Related Art
In an image formation apparatus employing electrophotography, it has been difficult to form a uniform high-gloss image as created by silver halide photography. The high-gloss image has a smooth surface and it is necessary to sufficiently fuse toner having a particle size not less than 5 μm so as to obtain such a surface. However, when the toner is sufficiently fused, a fixing method using a conventional fixing roller and a fixing belt poses problems such as hot offset where the toner is adhered to the fixing roller and winding where the recording material is wound around the fixing roller. Further, there is another problem in that while the toner is fused at high temperature, when a toner surface is separated from the fixing roller or the fixing belt, a surface shape is deformed and a smooth high-gloss image is not provided.
Patent Documents 1 and 2 disclose methods for obtaining a uniform high-gloss image so as to solve the above-mentioned problems. In techniques disclosed in Patent Documents 1 and 2, the gloss-providing sheet is placed on the toner image fixed on the recording material and then heated and pressurized again, so that the toner image is sufficiently re-fused and the gloss-providing sheet is separated after the toner is cooled and solidified, thereby obtaining high gloss. An important point here is to separate the gloss-providing sheet after the toner is cooled and solidified. In accordance with this, a shape of a smooth sheet surface is transferred to the toner surface and the toner surface becomes smooth, so that it is possible to obtain a uniform high-gloss image.
Patent Document 3 discloses a more advanced technique. In the technique disclosed in Patent Document 3, a heating portion, cooling portion, and separation portion are disposed on a circumference of an endless belt. The heating portion sufficiently fuses the toner, the cooling portion subsequently cools and solidifies the toner so as to transfer a smooth surface shape of the endless belt to the toner, and then the separation portion performs separation, thereby obtaining a uniform high-gloss image.
It is possible to increase gloss of a solid portion by sufficiently fusing the toner and having a smooth surface. However, on a halftone made of dots or lines, it is impossible to form a uniform high-gloss image since fields where the toner is placed and where the toner is not placed are mixed and convexity and concavity are inevitably formed on the surface.
In view of this, as disclosed in Patent Document 4, there is a method employing a recording material in which a layer coated with thermoplastic resin is disposed on the surface and the toner is embedded in the coated layer, so that a smooth surface is obtained.
At convenience stores and the like, there are disposed products as digital camera printers capable of forming a uniform high-gloss image as created by silver halide photography in combination with the technique disclosed in Patent Document 3 and the technique disclosed in Patent Document 4.
Further, a large number of electrophotographic image formation apparatuses including a laminating function have been proposed (refer to Patent Document 5, for example). However, these apparatuses have little practical use since any of such apparatuses requires a large-scale device and some users do not prefer laminated images, so that such apparatuses have been hardly used.
In an image formation apparatus employing electrophotography, it has been difficult to form a uniform high-gloss image as created by silver halide photography largely because toner having a particle size of not less than 5 μm is used when attempting to have a smooth surface for an image. It is possible to increase gloss of a solid portion by sufficiently fusing the toner and having a smooth surface. However, on a halftone made of dots or lines, it is impossible to form uniformly high-gloss since fields where the toner is placed and where the toner is not placed are mixed and convexity and concavity are inevitably formed on the surface.
In view of this, as disclosed in Patent Document 4, a recording material has been used such that a layer coated with thermoplastic resin is disposed on the surface and the toner is embedded in the coated layer, so that a smooth surface is obtained. However, even when this recording material is used, a fixing method for a conventional fixing device using a fixing roller and a fixing belt poses problems such as hot offset where the toner is adhered to the fixing roller when the toner is sufficiently fused and winding where the recording material is wound around the fixing roller. Further, there is another problem in that while the toner is fused at high temperature, when a toner surface is separated from the fixing roller or the fixing belt, a surface shape is deformed and a smooth high-gloss image is not provided.
In view of this, as disclosed in Patent Document 6, there is proposed a fixing device in which a heating portion, cooling portion, and separation portion are disposed on a circumference of an endless belt having a smooth high-gloss surface. In the device, the heating portion sufficiently fuses the toner so as to follow the gloss surface, the cooling portion solidifies the toner so as to transfer the gloss surface of the endless belt, and then the separation portion separates the endless belt and the toner surface. In accordance with this, a smooth toner surface is obtained and a smooth high-gloss image is provided as a result.
In fact, this fixing device has been successfully commercialized and-disposed as digital camera printers at convenience stores and the like. However, this method requires a large-scale device, so that there are problems in terms of cost and size.
Further, as disclosed in Patent Documents 5 and 7, a large number of electrophotographic image formation apparatuses including a laminating function have been proposed. However, these apparatuses have little practical use since any of such apparatuses requires a large-scale device and some users do not prefer laminated images, so that such apparatuses have been hardly used.
Patent Document 1: Japanese Laid-Open Patent Application No. 4-31389
Patent Document 2: Japanese Laid-Open Patent Application No. 4-31393
Patent Document 3: Japanese Patent No. 2992711
Patent Document 4: Japanese Laid-Open Patent Application No. 63-92965
Patent Document 5: Japanese Laid-Open Patent Application No. 9-150456
Patent Document 6: Japanese Laid-Open Patent Application No. 2002-91048
Patent Document 7: Japanese Patent No. 3213969
The fixing device as proposed in Patent Document 3 has merits, in which the heating portion, cooling portion, and separation portion are disposed on the circumference of the endless belt. However, the fixing device has problems in that cost is increased, print speed cannot become fast because of the necessity of cooling time, and the belt has life resulting from degradation of the gloss surface of the belt because a structure of the device is different from that of a conventional fixing device.
By contrast, the methods proposed in Patent Documents 1 and 2 in which the sheet is placed become very simple when the recording material to which the gloss-providing sheet is adhered is output and a user separates the gloss-providing sheet since a conventional image formation apparatus is not largely modified. The methods have merits in that it is possible to use the structure of the conventional fixing device at low cost, it is possible to perform output at high speed without having the cooling time for solidifying the toner, and the problem of product life is eliminated by using a disposable gloss-providing sheet or replacing the belt with a new one when the gloss surface is degraded.
However, when the gloss-providing sheet is separated, if the user erroneously separates the sheet while the toner is not sufficiently cooled and solidified, a smooth surface of the toner is deformed and a uniform high-gloss image is not obtained. Accordingly, the user is required to separate the sheet after sufficient cooling, so that it is necessary to notify the user of a time when the user is allowed to separate the sheet.
Further, in order to solve the problem that while the toner is fused at high temperature, when the toner surface is separated from the fixing roller or the fixing belt, the surface shape is deformed and a smooth high-gloss image is not provided, as disclosed in Patent Document 6, it is necessary to cool and solidify the toner before separating the toner surface after the toner is fused to follow the smooth high-gloss surface.